Ákos Császár (, ) (26 February 1924 – 14 December 2017) was a Hungarian mathematician, specializing in

general topology In mathematics, general topology (or point set topology) is the branch of topology that deals with the basic set-theoretic definitions and constructions used in topology. It is the foundation of most other branches of topology, including differ ...

and

real analysis In mathematics, the branch of real analysis studies the behavior of real numbers, sequences and series of real numbers, and real functions. Some particular properties of real-valued sequences and functions that real analysis studies include co ...

. He discovered the Császár polyhedron, a nonconvex

polyhedron In geometry, a polyhedron (: polyhedra or polyhedrons; ) is a three-dimensional figure with flat polygonal Face (geometry), faces, straight Edge (geometry), edges and sharp corners or Vertex (geometry), vertices. The term "polyhedron" may refer ...

without diagonals. He introduced the notion of syntopogeneous spaces, a generalization of

topological space In mathematics, a topological space is, roughly speaking, a Geometry, geometrical space in which Closeness (mathematics), closeness is defined but cannot necessarily be measured by a numeric Distance (mathematics), distance. More specifically, a to ...

s. He was born in

Budapest Budapest is the Capital city, capital and List of cities and towns of Hungary, most populous city of Hungary. It is the List of cities in the European Union by population within city limits, tenth-largest city in the European Union by popul ...

. Towards the end of 1944 his grandfather lost his life during the

Siege of Budapest The siege of Budapest or battle of Budapest was the 50-day-long encirclement by Soviet and Romanian forces of the Hungarian capital of Budapest, near the end of World War II. Part of the broader Budapest Offensive, the siege began when Budapes ...

. Then his father, older brother and himself were arrested by the Germans and sent to a concentration camp approximatively 45 miles east of Budapest. An infectious illness spread in the camp, and his brother and father died, but Ákos survived. He was a member of the group of five students of the late professor

Lipót Fejér Lipót Fejér (or Leopold Fejér, ; 9 February 1880 – 15 October 1959) was a Hungarian mathematician of Jewish heritage. Fejér was born Leopold Weisz, and changed to the Hungarian name Fejér around 1900. Biography He was born in Pécs, Au ...

, who called them "The Big Five". The other four are John Horvath, János Aczél, Steven Gaal, and

László Fuchs László Fuchs (born June 24, 1924) is a Hungary, Hungarian-born American mathematician, the Evelyn and John G. Phillips Distinguished Professor Emeritus in Mathematics at Tulane University.

, all of whom became mathematics professors in North America;Tribute to the achievements of five outstanding Hungarian mathematicians
Department of Mathematical Sciences of the Hungarian Academy of Sciences of that group, only Császár became a university professor in Budapest. Between 1952 and 1992 he was head of the Department of Analysis at the

Eötvös Loránd University Eötvös Loránd University (, ELTE, also known as ''University of Budapest'') is a Hungarian public research university based in Budapest. Founded in 1635, ELTE is one of the largest and most prestigious public higher education institutions in ...

in Budapest. He was elected corresponding member (1970), and then full member (1979) of the

Hungarian Academy of Sciences The Hungarian Academy of Sciences ( , MTA) is Hungary’s foremost and most prestigious learned society. Its headquarters are located along the banks of the Danube in Budapest, between Széchenyi rakpart and Akadémia utca. The Academy's primar ...

. He was general secretary (1966–1980), president (1980–1990), and honorary president (after 1990) of the

János Bolyai Mathematical Society The János Bolyai Mathematical Society (Bolyai János Matematikai Társulat, BJMT) is the Hungarian mathematical society, named after János Bolyai, a 19th-century Hungarian mathematician, a co-discoverer of non-Euclidean geometry. It is the profe ...

. He received the

Kossuth Prize The Kossuth Prize (, ) is a state-sponsored award in Hungary, named after the Hungarian politician and revolutionist Lajos Kossuth. The Prize was established in 1936, by the Hungarian National Assembly, to acknowledge outstanding personal and grou ...

(1963) and the Gold Medal of the Hungarian Academy of Sciences (2009). Császár died in Budapest on 14 December 2017, aged 93.

Selected publications

* Á. Császár: A polyhedron without diagonals, '' Acta Scientiarum Mathematicarum'', 13 (1949), 140–142. * Á. Császár: ''Foundations of general topology'',

Pergamon Press Pergamon Press was an Oxford-based publishing house, founded by Paul Rosbaud and Robert Maxwell, that published scientific and medical books and journals. Originally called Butterworth-Springer, it is now an imprint of Elsevier. History The c ...

, The Macmillan Co., New York 1963 xix+380 pp., translated from ''Fondements de la topology générale'', Akadémiai Kiadó, Budapest (1960) 231 pp. * Á. Császár: ''General topology'', Translated from the Hungarian by Klára Császár. Adam Hilger Ltd., Bristol, 1978. 488 pp.

References

1924 births 2017 deaths Mathematicians from Budapest Topologists 20th-century Hungarian mathematicians 21st-century Hungarian mathematicians Members of the Hungarian Academy of Sciences {{Europe-mathematician-stub